A general structure of a head to be used for a liquid discharge recording includes a structure having a plurality of discharge ports, a flow path which communicates with the discharge ports, and a plurality of heat generating resistive elements for generating thermal energy used for discharging a liquid. The heat generating resistive element is structured so as to have a heat generating resistive element and an electrode for supplying an electric power to the heat generating resistive element. Insulation properties between each heat generating resistive element are secured by covering the heat generating resistive elements with an insulation film. The discharge port and an opposite end of each liquid flow path are communicated with a common liquid chamber, and a liquid is stored in the common liquid chamber, which is supplied from a liquid tank of a liquid-storing section. The liquid which has been supplied to the common liquid chamber is introduced into each liquid flow path from the common liquid chamber, and is retained in the vicinity of the discharge port in a state of forming a meniscus. The liquid discharge head selectively drives the heat generating resistive element in the state, rapidly heats and bubbles a liquid on a thermal action face by using thereby generated thermal energy, and discharges the liquid by using the pressure according to the change of the state.
When the liquid is discharged, the thermal action portion of the liquid discharge head is exposed to high temperature due to heat generated by the heat generating resistive element, and results in receiving a cavitation impact due to the bubbling and retraction of the liquid in combination with a chemical action by the liquid.
Therefore, an upper protective layer is usually provided on the thermal action portion so as to protect the heat generating resistive element from the cavitation impact and the chemical action by the liquid.
A method for manufacturing a liquid discharge head using the base for a head, which has such an upper protective layer formed thereon, is disclosed in U.S. Pat. No. 5,478,606, for instance.
Conventionally, a Ta film which is comparatively resistant to the cavitation impact and the chemical action by the liquid has been formed on the surface of the thermal action portion into a thickness of 0.2 to 0.5 μm as the upper protective layer, in order to balance the lifetime of the head with the reliability.
On these thermal action portions, such a phenomenon has occurred that a color material, an additive or the like contained in the liquid is decomposed into a molecular level by being heated at high temperature, is changed into a substance having poor solubility, and is physically absorbed onto the upper protective layer. This phenomenon is referred to as kogation.
When an organic substance and an inorganic substance having poor solubility are absorbed on the upper protective layer in this way, thermal conductance to the liquid from the heat generating resistive element becomes ununiform, and the liquid is bubbled unstably. For this reason, a Ta film is generally used which causes comparatively little kogation thereon and is an adequate film.
A behavior of the liquid in relation with bubbling and debubbling on a thermal action portion is described with reference to FIG. 7. FIG. 7 is a view for describing a temperature change of an upper protective layer and a state of bubbling occurring after voltage has been applied.
A curve (a) of FIG. 7 shows a change of a surface temperature of the upper protective layer with time occurring after the moment when voltage has been applied to a heat generating resistive element in driving conditions of driving voltage (Vop): 1.3×Vth (Vth: bubbling threshold voltage of liquid), driving frequency: 6 kHz, and pulse width: 5 μs. In addition, a curve (b) similarly shows a growing state of a bubble occurring after the moment when the voltage has been applied to the heat generating resistive element.
As is shown in the curve (a), the temperature starts to increase after the voltage has been applied, reaches a peak of the temperature slightly later than a predetermined pulse time which has been set (because heat from the heat generating resistive element reaches to the upper protective layer slightly later), and afterwards decreases mainly through thermal diffusion. On the other hand, as shown in the curve (b), the bubble starts growing when the temperature of the upper protective layer approaches about 300° C., and debubbles after having reached the maximum bubbling state. In an actual liquid discharge head, the above process is repeated. Thus, the surface of the upper protective layer increases, for instance, to approximately 600° C. along with the bubbling of the liquid, and it is understood that liquid discharge recording is carried out along with a thermal action of very high temperature.
Accordingly, an upper protective layer which contacts the liquid is required to have film characteristics superior in heat resistance, mechanical properties, chemical stability, oxidation resistance, alkali resistance and the like. A noble metal, a high-melting transition metal or the like in addition to the above Ta film is used as a material to be used in the upper protective layer.
However, in recent years, higher functions such as high image quality and high speed record are further demanded to the liquid discharge recording. In order to satisfy these demands, the liquid discharge recording is required to improve an ink performance, for instance, color developing properties and weathering resistance so as to cope with the tendency of higher image quality, and to prevent bleeding (bleed between different color inks) so as to cope with a high-speed recording. Then, in order to satisfy these requirements, such attempts have been made as to add various components into an ink. In addition, a type of ink itself is diversified. For instance, inks of a pale color having a thinned concentration in addition to black, yellow, magenta and cyan are used. Even a Ta film which has been conventionally considered to have stability against these inks as the upper protective layer causes a phenomenon of corrosion due to a thermochemical reaction with the inks. The phenomenon remarkably appears when the used ink contains, for instance, a salt of a bivalent metal such as Ca and Mg, or a component of forming a chelate complex.
On the other hand, when a formed upper protective layer has an improved corrosion resistance against the ink as described above, the upper protective layer shows high corrosion resistance, but on the contrary, tends to easily cause kogation because the surface is little damaged. Thereby, the discharge speed of the ink decreases and becomes unstable.
Incidentally, the reason why a conventionally used Ta film causes little kogation is because the occurrences of the slight corrosion of the Ta film and the kogation are well balanced. The reason is assumed to be because when the surface of the Ta film is scraped off by the corrosion, the deposits of products originating from the kogation are also removed from the surface of the Ta film, at the same time.
In order to further increase the speed of the liquid discharge recording, it is necessary to drive the liquid discharge head by increasing a driving frequency in comparison with a conventional one and using a shorter pulse. When the head is driven by such a short pulse, cycles of heating→bubbling→debubbling→cooling are repeated on a thermal action portion of the head in a short period of time, so that the thermal action portion receives more thermal stresses in a shorter period of time than the conventional one. When the head is driven by the short pulse, a cavitation impact originating from the bubbling and retraction of the ink is also concentrated on the upper protective layer in a shorter period of time than the conventional one. Therefore, the upper protective layer needs to have superior mechanical impact characteristics.
As for such an upper protective layer, U.S. Pat. No. 7,306,327 discloses a base for a liquid discharge head using a TaCr alloy of an amorphous structure including 12 at. % or more Cr.
In addition, U.S. Pat. No. 7,306,327 discloses a base for a liquid discharge head, which uses a TaCr alloy of an amorphous structure including 30 at. % or less Cr, because the alloy is easily patterned with a dry etching technique.
However, as the tendency of recording a recording image at a higher speed progresses recently, it is considered that a base for a liquid discharge head will be lengthened (into 1.0 inch or longer in particular), and that an ink containing an additive for enhancing the light resistance and gas resistance of the ink will be adopted. In this case, the stress or the like of a resin layer which forms a wall of a liquid flow path and a discharge port may cause distortion due to a difference of a linear expansion coefficient among the structural members of the head, and a component of a new ink may give influence to the interface between the structural members. From the above factors, it might happen that the flow path forming member made from a resin, which forms the wall of the liquid flow path and the discharge port is peeled from an upper protective layer on a silicon substrate. It was also likely to happen that even though an adhesion layer made from an organic substance would be provided on the upper protective layer so as to enhance the adhesiveness between the member and the layer, the upper protective layer is peeled from the adhesion layer in the vicinity of the interface between the layers, the ink infiltrates into a substrate side from the protective layer, and consequently causes the corrosion of wiring. As a result, it was likely to happen that an adequate recording is not obtained, and that quality reliability is difficult to be secured over a long period of time.
In other words, when the base had a size of 0.5 inches or more and less than 1.0 inch, the adhesiveness was adequate between a TaCr film and an adhesion layer of an organic substance disclosed in U.S. Pat. No. 5,478,606. However, a substrate of a lengthened recording device having a base size of 1 inch or more is required to have an upper protective layer therein which has a further enhanced adhesiveness.
As is disclosed in U.S. Pat. No. 7,306,327, when the TaCr film is patterned with a generally used dry etching technique, the etching rate depends on a Cr content, and decreases as the Cr content increases.